Formulation of roselle extract water-in-oil nanoemulsion for controlled pulmonary delivery

The anthocyanin (ACN)-rich roselle extract has the potential to inhibit lung cancer. However, the compounds demonstrate low bioavailability and stability in biological applications. The present study proposed a stable formulation of a water-in-oil (w/o) roselle extract nanoemulsion by combining low (hot temperature inversion) and high-energy approaches (ultrasonication and ultra-homogenization) for pulmonary delivery. The stable w/o formulation comprised of roselle extract (0.04 w/w%), sodium chloride solution (3.0 w/w%), medium-chain triglyceride (81.9 w/w%), surfactant (Tween 80 and Span 80) (15.0 w/w%), hydrophilic-lipophilic balance (HLB) of 6.7 [Tween 80/Span 80 (22.5:77.5)] to yield the stable nanoemulsion.The best nanoemulsion showed an average 298 nm particle size, polydispersity index of 0.6, and zeta potential of -49.0 mV. The emulsions were stable in the centrifuge- and freeze-thaw cycle tests,-alongside the 60-days storage tests at 4 degrees C, 25 degrees C, and 35 degrees C. The in-vitro release of the roselle extract at pH 6.5 buffer was 44.7% and 40.7% at pH 7.4 (p > 0.05), with the release patterns following the non-Fickian diffusion. Hence, the present study successfully developed a stable w/o roselle extract nanoemulsion with a relatively moderate release rate of the ACNs, supporting its suitability as a nanocarrier for pulmonary delivery.